The invention is related to superconducting wire having at least one filament of superconducting material. More particularly, the invention relates to a multi-filament superconducting wire comprising a zirconia-stabilized, niobium tin superconductor and a matrix material, and a method of making such a multi-filament superconducting wire.
Superconducting wires comprising multiple filaments of niobium-based superconductors, such as niobium tin (hereinafter referred to as xe2x80x9cNb3Snxe2x80x9d), are used in a variety of electromagnetic applications, such as magnets, motors, and transformers. To maintain sufficient critical current density in the superconducting wire during operation at cryogenic temperatures of less than 17.5 K, the Nb3Sn comprising filaments within the wire must have an ultra-fine grain size of less than about 1 micron. One of the processes that is used to manufacture multi-filament Nb3Sn wire is the xe2x80x9cbronze process,xe2x80x9d in which ultra-fine grains of Nb3Sn are formed on the surface of wire-drawn niobium filaments by heat treatment for several days at relatively low temperatures.
The length of the heat treatment required to produce ultra-fine grain Nb3Sn is exceedingly time-intensive and uneconomical. Therefore, what is needed is a superconducting wire comprising ultra-fine grain Nb3Sn that is formed by a more rapid process. What is also needed is a method of more rapidly making a multi-filament superconducting wire comprising ultra-fine grained Nb3Sn.
The present invention meets these and other needs by providing a multi-filament superconducting wire in which the filaments comprise zirconia-stabilized ultra-fine grained (also referred to hereinafter as xe2x80x9cUFGxe2x80x9d) Nb3Sn. The superconducting wire is formed by deformation processing of a preform comprising a metallic matrix and at least one niobium alloy rod having precipitates of zirconia, also known as zirconium oxide and hereinafter referred to as xe2x80x9cZrO2. xe2x80x9d The ZrO2 precipitates serve to stabilize the ultra-fine grained microstructure of the Nb3Sn at temperatures up to 1100xc2x0 C. and allows Nb3Sn to maintain the ultra-fine grained microstructure when heat treated at temperatures that are greater than those previously used. By using higher temperatures to form Nb3Sn, the time required for heat treatment can be significantly reduced.
Accordingly, one aspect of the invention is to provide a superconducting wire. The superconducting wire comprises: at least one filament having a filament diameter, wherein the at least one filament is continuous and comprises a plurality of Nb3Sn grains having a plurality of ZrO2 precipitates disposed therein, and wherein the plurality of Nb3Sn grains have an average grain size of less than about 10 percent of the filament diameter; and a metallic matrix surrounding and contacting the at least one filament, wherein the metallic matrix is electrically conductive at temperatures below about 77 K and has a coefficient of thermal expansion that is substantially the same as or greater than that of Nb3Sn.
A second aspect of the invention is to provide a preform for forming a superconducting wire comprising at least one filament having a filament diameter, wherein the at least one filament comprises a plurality of Nb3Sn grains having a plurality of ZrO2 precipitates disposed therein and a metallic matrix surrounding and contacting the at least one filament. The preform comprises: at least one niobium alloy rod comprising a niobium alloy having oxygen and zirconium in solid solution, wherein zirconium and oxygen are present in an atomic ratio of about 1:2; and a metallic preform matrix surrounding and contacting the at least one niobium alloy rod, wherein the metallic preform matrix comprises tin.
A third aspect of the invention is to provide a superconducting wire, formed from a preform comprising at least one niobium alloy rod comprising a niobium alloy having oxygen and zirconium in solid solution, wherein zirconium and oxygen are present in an atomic ratio of about 1:2, and a metallic preform matrix surrounding and contacting the at least one niobium alloy rod, wherein the metallic preform matrix comprises tin. The superconducting wire comprises: a plurality of filaments, wherein each of the plurality of filaments is continuous and has a filament diameter, wherein at least one filament comprises a plurality of Nb3Sn grains having a plurality of ZrO2 precipitates disposed therein, and wherein the plurality of Nb3Sn grains has an average grain size of less than about 10 percent of the filament diameter; and a metallic matrix surrounding and contacting the plurality of filaments, wherein the metallic matrix is electrically conductive at temperatures below about 77 K and has a coefficient of thermal expansion that is substantially the same as or greater than that of Nb3Sn.
A fourth aspect of the invention is to provide an electromagnetic device comprising at least one superconducting wire, wherein the superconducting wire is formed from a preform comprising at least one niobium alloy rod comprising a niobium alloy having oxygen and zirconium in solid solution, wherein zirconium and oxygen are present in an atomic ratio of about 1:2, and a metallic preform matrix surrounding and contacting the at least one niobium alloy rod, and wherein the metallic preform matrix comprises tin. The superconducting wire comprises: a plurality of filaments, wherein each of the plurality of filaments has a filament diameter, wherein at least one filament is continuous and comprises a plurality of Nb3Sn grains having a plurality of ZrO2 precipitates disposed therein, wherein the plurality of Nb3Sn grains has an average grain size of less than about 10 percent of the filament diameter; and a metallic matrix surrounding and contacting the plurality of filaments, and wherein the metallic matrix is electrically conductive at temperatures below about 77 K and has a coefficient of thermal expansion that is substantially the same as or greater than that of Nb3Sn.
A fifth aspect of the invention is to provide a method of making a superconducting wire comprising at least one filament, wherein the at least one filament is continuous and comprises a plurality of Nb3Sn grains having a plurality of ZrO2 precipitates disposed therein and a metallic matrix surrounding and contacting the at least one filament. The method comprises the steps of: providing a niobium alloy having oxygen and zirconium in solid solution, wherein zirconium and oxygen are present in an atomic ratio of about 1:2; forming at least one niobium alloy rod from the niobium alloy; providing a metallic matrix material to the at least one niobium alloy rod; forming a wire from the metallic matrix material and the at least one niobium alloy rod; and heat treating the wire at a predetermined temperature for a predetermined time, thereby forming the superconducting wire.
A sixth aspect of the invention is to provide a method of making a preform for a superconducting wire comprising at least one niobium alloy rod having oxygen and zirconium in solid solution, wherein zirconium and oxygen are present in an atomic ratio of about 1:2, and a metallic preform matrix surrounding and contacting the at least one niobium alloy rod. The method comprises the steps of: providing a niobium alloy having oxygen and zirconium in solid solution, wherein zirconium and oxygen are present in an atomic ratio of about 1:2; forming at least one niobium alloy rod from the niobium alloy; providing a metallic matrix material to the at least one niobium alloy rod; and forming a preform by surrounding the at least one niobium alloy rod with the metallic matrix material such that the metallic matrix material contacts the at least one niobium alloy rod.
A seventh aspect of the invention is to provide a superconducting wire comprising: at least one filament having a filament diameter, wherein the at least one filament is continuous and comprises a plurality of Nb3Sn grains having a plurality of ZrO2 Sn precipitates disposed therein, wherein the plurality of Nb3Sn grains have an average grain size of less than about 10 percent of the filament diameter; and a metallic matrix surrounding and contacting the at least one filament, wherein the metallic matrix has a coefficient of thermal expansion that is substantially the same as or greater than that of Nb3Sn, and wherein the superconducting wire is formed by: providing a niobium alloy having oxygen and zirconium in solid solution, wherein zirconium and oxygen are present in an atomic ratio of about 1:2; forming at least one niobium alloy rod from the niobium alloy; providing a metallic matrix material to the at least one niobium alloy rod; forming a wire from the metallic matrix material and the at least one niobium alloy rod; and heat treating the wire at a predetermined temperature for a predetermined time to form the superconducting wire.